I’ve also got the Linux Basics for Hackers book but it’s at home while I’m on vacation.
I’m just really happy rn yall :) this install took some work, SecureBoot kept getting in the way and I’m not the most savvy person so there was a lot of Googling and trial and error in the way of getting here.
You don’t need to reinstall. You could keep the old partition and format it and add it as a new volume while keeping the current installation.
If the windows volume is to the right of the Linux volume, you could also boot a live-usb and drop the windows partition and then extend the Linux partition then extend the Linux filesystem to cover all disk space. If it is to the left, you can do the same but you’d need to move the partition and reinstall the bootloader as well.
A backup would be mandatory If you don’t really know what you would be doing with the above, however. But if you do, it’s a lot easier and faster than to rebuild everything from scratch.